Vitamin A-deficient Rats Research Articles

Vitamin A-Deficient Rats have Only Mild Changes in Jejunal Structure and Function

This study investigated the effect of clinical and subclinical vitamin A deficiency on intestinal structure and function in rats. Weanling male rats fed a vitamin A-deficient diet (VA-) for 40–42 or 60–63 d were compared with rats either pair-fed (PF) or with free access to the same diet supplemented with vitamin A (VA+). A reference (REF) group was fed a standard rat diet. Weight began to plateau in VA- rats after 42 d, becoming significantly different from PF rats at 60–63 d (P < 0.02). Diarrhea did not develop in any study group. VA- rats had clinical signs of vitamin A deficiency in the 60–63 d study, but not in the 40–42 d study. However, serum and liver retinol concentrations were negligible in all VA- rats. VA- rats in the 60–63 d study had significantly reduced villus height (P < 0.02), and sucrase and maltase activities (P < 0.02) compared with PF rats. There were no differences between VA- and PF rats in mucosal wet weights, protein and DNA concentrations, thymidine kinase activity and glucose transport. No differences were detected in the 40–42 d study for any variable measured. Because clinical vitamin A deficiency in rats causes only mild changes in intestinal structure and function, it is unlikely that these alterations alone are responsible for the interactions observed in epidemiological studies between vitamin A deficiency and diarrheal disease.

Replenishment of vitamin A for 7 days partially restored hepatic gene expressions altered by its deficiency in rats.

We investigated the effects of vitamin A (VA) status on metabolism of Zucker rats with different genders and genotypes, and of short-term refeeding of a VA sufficient (VAS) diet on VA deficient (VAD) animals. First, male and female Zucker lean (ZL) and fatty (ZF) rats at weaning were fed a VAD or VAS diet for 8 weeks. Second, male VAD ZL rats were fed a VAS diet for 3 (VAD-VAS3d) or 7 (VAD-VAS7d) days. The body weight (BW), blood parameters, and hepatic expressions of genes for metabolism were determined. VA deficiency reduced BW gain in ZL and ZF rats of either gender. VAD ZL rats had lower plasma glucose, insulin, and leptin levels than VAS ZL rats. VAD-VAS3d and VAD-VAS7d rats had higher plasma glucose, insulin, and leptin levels than that in the VAD rats. The hepatic mRNA levels of Gck, Cyp26a1, Srebp-1c, Igf1, Rarb, Rxra, Rxrg, Pparg, and Ppard were lowered by VA deficiency. Refeeding of the VAS diet for 3 days restored the Gck and Cyp26a1 expressions, and for 7 days restored the Gck, Cyp26a1, Igf1, and Rxrb expressions significantly. The 7-day VA replenishment partially restored the hepatic gene expressions and metabolic changes in VAD ZL rats.

Cod Liver Oil, but Not Retinoic Acid, Treatment Restores Bone Thickness in a Vitamin A-Deficient Rat.

Vitamin A plays a prominent role for maintaining optimal bone status, but its impact upon the bone in response to vitamin A deficiency is not well defined. The purpose of this study was to evaluate how replenishing vitamin A by either whole food cod liver oil (COD) or the active metabolite of vitamin A, retinoic acid (RA), altered bone thickness of vitamin A-deficient (VAD) rats. Weanling rats were administered a control diet (CTRL) or VAD diet for 9 weeks. This was followed by four weeks of treatment in which the VAD group was divided into the following 4 subgroups: (1) VAD (9 weeks)-VAD (4 weeks); (2) VAD-CTRL; (3) VAD-COD; and (4) VAD-RA. Compared to controls, VAD rats had thicker bones which showed marked dysplasia. VAD-rats treated with COD produced a thinner bone that was not significantly different from that of untreated rats. In contrast, RA did not significantly change the thicker bone, and also had significantly greater periosteal and endosteal osteoblast numbers compared to VAD-COD. Active osteoclasts were not detected in VAD rats, nor during the treatment period. These findings suggest that the abnormal bone thickness in VAD rats appears to be more effectively restored to bone thickness of untreated control rats when treated with COD.

All-trans retinoic acid reduces the transcriptional regulation of intestinal sodium-dependent phosphate co-transporter gene (Npt2b).

Inorganic phosphate (Pi) homeostasis is regulated by intestinal absorption via type II sodium-dependent co-transporter (Npt2b) and by renal reabsorption via Npt2a and Npt2c. Although we previously reported that vitamin A-deficient (VAD) rats had increased urine Pi excretion through the decreased renal expression of Npt2a and Npt2c, the effect of vitamin A on the intestinal Npt2b expression remains unclear. In this study, we investigated the effects of treatment with all-trans retinoic acid (ATRA), a metabolite of vitamin A, on the Pi absorption and the Npt2b expression in the intestine of VAD rats, as well as and the underlying molecular mechanisms. In VAD rats, the intestinal Pi uptake activity and the expression of Npt2b were increased, but were reduced by the administration of ATRA. The transcriptional activity of reporter plasmid containing the promoter region of the rat Npt2b gene was reduced by ATRA in NIH3T3 cells overexpressing retinoic acid receptor (RAR) and retinoid X receptor (RXR). On the other hand, CCAAT/enhancer-binding proteins (C/EBP) induced transcriptional activity of the Npt2b gene. Knockdown of the C/EBP gene and a mutation analysis of the C/EBP responsible element in the Npt2b gene promoter indicated that C/EBP plays a pivotal role in the regulation of Npt2b gene transcriptional activity by ATRA. EMSA revealed that the RAR/RXR complex inhibits binding of C/EBP to Npt2b gene promoter. Together, these results suggest that ATRA may reduce the intestinal Pi uptake by preventing C/EBP activation of the intestinal Npt2b gene.

Vitamin A supplementation improves the intestinal mucosal barrier and facilitates the expression of tight junction proteins in rats with diarrhea.

The aim of this study is to investigate the specific effects of vitamin A (VA) on diarrhea in rats and its potential targets to protect the intestinal mucosa. Specific pathogen-free Sprague Dawley rats were fed a VA deficient (VAD) or VA normal (VAN) diet for 4 wk. Then, half of the VAN rats were treated with a VAN diet and the other half with a lactose VAN diet. VAD rats were randomly assigned to one of four groups and fed a VAD diet, lactose VAD diet, VAN diet with VA supplementation (VAS) via daily intragastric administration, or a lactose VAN diet with daily VAS. Rat weight and degree of diarrhea were evaluated daily. After 15 d, the serum retinol level was measured by high-performance liquid chromatography, and the serum diamine oxidase (DAO) and zonulin concentrations were analyzed by enzyme-linked immunosorbent assays. The small intestine mucosal pathology was observed by hematoxylin and eosin staining. Western blotting was performed to detect the protein expression levels of occludin and claudin-1 in the intestinal mucosa, and the zonula-occludens 1 expression was assessed using immunohistochemistry. VAD limited weight gain in rats and increased the degree of diarrhea. The serum retinol levels and the level of tight junction (TJ) proteins claudin-1 and occludin and grip strength were affected by the interaction between lactose-induced diarrhea and the VA diet. Diarrhea, independent of VAD, significantly decreased rat weight, increased serum DAO levels, damaged small intestine villi, and impaired zonula-occludens 1 protein expression. VAD significantly increased the concentration of zonulin independently of diarrhea, but VAS increased the serum retinol level, reduced the severity of diarrhea, increased the expression levels of the TJ proteins, facilitated the restoration of the small intestine villi that were damaged by the diarrhea, and decreased the concentrations of serum DAO and zonulin. VAD may aggravate the degree of diarrhea and intestinal mucosal damage during the duration of diarrhea, and VAS helps relieve diarrhea and improves intestinal damage likely by regulating the expression of TJ proteins. Therefore, VA plays a pivotal role in the protection of the intestinal mucosa during instances of diarrhea.

Isolation of lactobacillus reuteri from Peyer's patches and their effects on sIgA production and gut microbiota diversity.

We previously reported that specific Lactobacillus reuteri colonized within mouse Peyer's patches (PP) effectively prevented high fat diet induced obesity and low-grade chronic inflammation. We further investigated the role of PP Lactobacillus reuteri on sIgA production in rats in this study. Lactobacilli were isolated from rat PP. All isolates were L. reuteri and belonged to three phenotypes according to amplified fragment length polymorphism analysis. Typical strains of two main clusters, PP1 and PP2, were used to treat control and vitamin A deficient (VAD) rats, respectively. The feeding of PP1 and PP2 affected sIgA and Lactobacillus diversity by strain-specific manner. Free sIgA was significantly increased by PP1 (p = 0.069) and PP2 (p < 0.05) in the control rats but not in the VAD rats. Only PP1 significantly changed PP Lactobacillus diversity in the control rats (p < 0.05). However, PP2 specifically changed ileal Lactobacillus diversity in both control and VAD rats. Fecal sIgA was correlated with PP Lactobacillus diversity (R(2) = 0.7958, p = 0.011). Modulation of sIgA production by PP L. reuteri of rat is dependent on vitamin A and change of Lactobacillus diversity in PP.

The Alterations in the Expression and Function of P-Glycoprotein in Vitamin A-Deficient Rats as well as the Effect of Drug Disposition in Vivo

This study was aimed to investigate whether vitamin A deficiency could alter P-GP expression and function in tissues of rats and whether such effects affected the drug distribution in vivo of vitamin A-deficient rats. We induced vitamin A-deficient rats by giving them a vitamin A-free diet for 12 weeks. Then, Abcb1/P-GP expression was evaluated by qRT-PCR and Western blot. qRT-PCR analysis revealed that Abcb1a mRNA levels were increased in hippocampus and liver. In kidney, it only showed an upward trend. Abcb1b mRNA levels were increased in hippocampus, but decreased in cerebral cortex, liver and kidney. Western blot results were in good accordance with the alterations of Abcb1b mRNA levels. P-GP function was investigated through tissue distribution and body fluid excretion of rhodamine 123 (Rho123), and the results proclaimed that P-GP activities were also in good accordance with P-GP expression in cerebral cortex, liver and kidney. The change of drug distribution was also investigated through the tissue distribution of vincristine, and the results showed a significantly upward trend in all indicated tissues of vitamin A-deficient rats. In conclusion, vitamin A deficiency may alter Abcb1/P-GP expression and function in rat tissues, and the alterations may increase drug activity/toxicity through the increase of tissue accumulation.

AB210. Targeted disruption of the spermatid-specific gene Spata31 causes male infertility

Spata31, a novel testis-specific gene, was first isolated from the testis of a vitamin A-deficient rat model. To gain insight into its physiological function, Spata31-targeted knockout mice were generated by homologous recombination. Spata311-deficient [Spata31(flox/flox); Vasa-Cre] male mice exhibited low sperm count and premature shedding of germ cells into the lumen, ultimately causing azoospermia and male sterility. Mechanistically, the Spata31 deficiency resulted in reduced expression of the adhesion protein nectin-3 and cytoskeletal protein β-actin at the apical ectoplasmic specialization. Our findings demonstrate that the disruptions to the SPATA31 ortholog could be linked to human male infertility.

Targeted disruption of the spermatid-specific gene Spata31 causes male infertility.

Spata31, a novel testis-specific gene, was first isolated from the testis of a vitamin A-deficient rat model. To gain insight into its physiological function, Spata31-targeted knockout mice were generated by homologous recombination. Spata31-deficient (Spata31(flox/flox) ; Vasa-Cre) male mice exhibited low sperm count and premature shedding of germ cells into the lumen, ultimately causing azoospermia and male sterility. Mechanistically, the Spata31 deficiency resulted in reduced expression of the adhesion protein nectin-3 and cytoskeletal protein β-actin at the apical ectoplasmic specialization. Our findings demonstrate that the disruptions to the SPATA31 ortholog could be linked to human male infertility.

Vitamin A supplementation in early life enhances the intestinal immune response of rats with gestational vitamin A deficiency by increasing the number of immune cells.

Vitamin A is a critical micronutrient for regulating immunity in many organisms. Our previous study demonstrated that gestational or early-life vitamin A deficiency decreases the number of immune cells in offspring. The present study aims to test whether vitamin A supplementation can restore lymphocyte pools in vitamin A-deficient rats and thereby improve the function of their intestinal mucosa; furthermore, the study aimed to identify the best time frame for vitamin A supplementation. Vitamin A-deficient pregnant rats or their offspring were administered a low-dose of vitamin A daily for 7 days starting on gestational day 14 or postnatal day 1, day 14 or day 28. Serum retinol concentrations increased significantly in all four groups that received vitamin A supplementation, as determined by high-performance liquid chromatography. The intestinal levels of secretory immunoglobulin A and polymeric immunoglobulin receptor increased significantly with lipopolysaccharide challenge in the rats that received vitamin A supplementation starting on postnatal day 1. The rats in this group had higher numbers of CD8+ intestinal intraepithelial lymphocytes, CD11C + dendritic cells in the Peyer's patches and CD4+CD25+ T cells in the spleen compared with the vitamin A-deficient rats; flow cytometric analysis also demonstrated that vitamin A supplementation decreased the number of B cells in the mesenteric lymph nodes. Additionally, vitamin A supplementation during late gestation increased the numbers of CD8+ intestinal intraepithelial lymphocytes and decreased the numbers of B lymphocytes in the mesenteric lymph nodes. However, no significant differences in lymphocyte levels were found between the rats in the other two vitamin A supplement groups and the vitamin A-deficient group. In conclusion, the best recovery of a subset of lymphocytes in the offspring of gestational vitamin A-deficient rats and the greatest improvement in the intestinal mucosal immune response are achieved when vitamin A supplementation occurs during the early postnatal period.

Vitamin A regulates hypothalamic–pituitary–adrenal axis status in LOU/C rats

The aim of this study was to explore the involvement of retinoids in the hypoactivity and hyporeactivity to stress of the hypothalamic-pituitary-adrenal (HPA) axis in LOU/C rats. We measured the effects of vitamin A deficiency administered or not with retinoic acid (RA) on plasma corticosterone in standard conditions and in response to restraint stress and on hypothalamic and hippocampal expression of corticosteroid receptors, corticotropin-releasing hormone and 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in LOU/C rats. Interestingly, under control conditions, we measured a higher plasma concentration of retinol in LOU/C than in Wistar rats, which could contribute to the lower basal activity of the HPA axis in LOU/C rats. Vitamin A deficiency induced an increased HPA axis activity in LOU/C rats, normalized by RA administration. Compared with LOU/C control rats, vitamin A-deficient rats showed a delayed and heightened corticosterone response to restraint stress. The expression of corticosteroid receptors was strongly decreased by vitamin A deficiency in the hippocampus, which could contribute to a less efficient feedback by corticosterone on HPA axis tone. The expression of 11β-HSD1 was increased by vitamin A deficiency in the hypothalamus (+62.5%) as in the hippocampus (+104.7%), which could lead to a higher production of corticosterone locally and contribute to alteration of the hippocampus. RA supplementation treatment restored corticosterone concentrations and 11β-HSD1 expression to control levels. The high vitamin A status of LOU/C rats could contribute to their low HPA axis activity/reactivity and to a protective effect against 11β-HSD1-mediated deleterious action on cognitive performances during ageing.

Changes on metabolic parameters induced by acute cannabinoid administration (CBD, THC) in a rat experimental model of nutritional vitamin A deficiency.

Vitamin A deficiency can result from malnutrition, malabsorption of vitamin A, impaired vitamin metabolism associated with liver disease, or chronic debilitating diseases like HIV infection or cancer. Cannabis administration has been described as a palliative symptom management therapy in such pathological stages. Therefore, this research aimed to study the effects of acute administration of cannabidiol (CBD) or thetrahydrocannabinol (THC) on the levels of retinol in plasma and in the liver, and biochemical parameters related to lipid and glucose metabolism (cholesterolaemia, triglyceridemia and glycemia) in a rat experimental model of vitamin A deficiency. The experimental animal model of Vitamin A deficiency was developed during a 50-day experimental period in which rats consumed a vitamin A-free diet. Cannabidiol (10 mg/kg body weight) or thetrahydrocannabinol (5 mg/kg body weight) were administered intraperitoneally 2 hours prior to sacrifice of the animals. The nutritional deficiency caused a significant decrease in plasmatic and liver contents of retinol and biochemical parameters of glycemic, lipidic, and mineral metabolism. Acute intraperitoneal administration of Cannabidiol and thetrahydrocannabinol did not improve the indices of vitamin A status in either control or vitamin A-deficient rats. However, it had a significant effect on specific biochemical parameters such as glucose, triglycerides, and cholesterol. Under our experimental conditions, the reported effects of cannabinoid administration on certain signs of nutritional vitamin A deficiency appeared to be mediated through mechanisms other than changes in retinol metabolism or its mobilization after the acute administration of such compounds.

Roles of dietary vitamin A in the regulation of hepatic gene expression in response to fasting‐refeeding cycle

We have shown that vitamin A (VA) status affects the plasma glucose and lipid levels, and hepatic gene expression in rats. Therefore, we hypothesize that dietary VA intake and its hepatic metabolism regulate the expression of genes involved in glucose and lipid metabolism in response to fasting‐refeeding cycle. Male Zucker lean rats were fed with a VA deficient (VAD) or a VA sufficient (VAS) diet for 8 weeks. The VAD or VAS rats were fed ad libitum, fasted for 48 hours (H) or refed a VAD or VAS diet for 6H. The plasma parameters were measured using commercial kits. The hepatic protein and mRNA levels were respectively examined by Western blot and real‐time PCR. The responses of plasma insulin and leptin levels to the feeding cycle were altered in VAD rats compared to VAS ones. The hepatic mRNA levels of Gck, Srebp‐1c, and Fas were reduced after 48H fasting regardless of VA status. The 6H refeeding of a VAS diet induced their mRNA levels in VAD and VAS rats. However, the 6H refeeding of a VAD diet only induced their expression levels in VAS, but not VAD rats. We conclude that dietary VA and its hepatic metabolism contribute to the regulation of plasma hormone levels and hepatic gene expression in rats.Grant Funding Source: American Heart Association

Vitamin A status affects obesity development and hepatic expression of key genes for fuel metabolism in Zucker fatty rats

We hypothesized that vitamin A (VA) status may affect obesity development. Male Zucker lean (ZL) and fatty (ZF) rats after weaning were fed a synthetic VA deficient (VAD) or VA sufficient (VAS) diet for 8 weeks before their plasma parameters and hepatic genes' expression were analyzed. The body mass (BM) of ZL or ZF rats fed the VAD diet was lower than that of their corresponding controls fed the VAS diet at 5 or 2 weeks, respectively. The VAD ZL and ZF rats had less food intake than the VAS rats after 5 weeks. The VAD ZL and ZF rats had lower plasma glucose, triglyceride, insulin, and leptin levels, as well as lower liver glycogen content, net mass of epididymal fat, and liver/BM and epididymal fat/BM ratios (ZL only) than their respective VAS controls. VAD rats had lower hepatic Cyp26a1, Srebp-1c, Fas, Scd1, Me1, Gck, and Pklr (ZL and ZF); and higher Igfbp1 (ZL and ZF), Pck1(ZF only), and G6pc (ZF only) mRNA levels than their respective VAS controls. We conclude that ZL and ZF rats responded differently to dietary VA deficiency. VA status affected obesity development and altered the expression of hepatic genes for fuel metabolism in ZF rats. The mechanisms will help us to combat metabolic diseases.

Subclinical vitamin A deficiency does not increase development of tumors in irradiated or unirradiated lungs.

Cancer patients often have subclinical vitamin A deficiencies and low vitamin A lung levels. Previous studies showed that subclinical vitamin A deficiency increased the severity of pneumonitis induced by whole-lung irradiation in rats. Many studies have shown that lung irradiation increases the number of lung tumors developing from intravenously injected tumor cells in mice. We examined the impact of vitamin A deficiency on the development of lung metastases from a highly metastatic syngeneic rat rhabdomyosarcoma in normal rats and rats receiving prior lung irradiation. Weanling female WAGrijY rats were randomized to receive either a diet lacking both vitamin A and beta-carotene or a control diet. After five weeks, the deficient diet significantly decreased levels of retinol in the lung and liver but not in the serum, modeling the tissue and blood levels seen in prior studies of patients with subclinical vitamin A inadequacy. The vitamin A-deficient diet did not alter the number of lung tumors developing from intravenously injected tumor cells in unirradiated rats. Whole-lung irradiation produced dose-dependent increases in the number of lung tumors developing from tumor cells injected intravenously one or 29 d after irradiation. Vitamin A deficiency did not alter these dose-response curves, indicating that the more intense radiation-induced pneumonitis seen previously in vitamin A-deficient rats did not alter the enhancement of metastases produced by whole-lung irradiation. Moreover, inadequate vitamin A intake did not influence the growth of tumors implanted subcutaneously or increase the number or size of the spontaneous lung metastases developing from these subcutaneous tumors. Thus, although low vitamin A status influences the development of lung injury and is considered a possible modifiable risk factor increasing risk of primary cancer, it did not affect the growth of subcutaneous tumors or increase the development of artificial or spontaneous lung metastases in this rat model.

A close relationship between type 1 diabetes and vitamin A-deficiency and matrix metalloproteinase and hyaluronidase activities in skin tissues

Numerous wrinkles are observed in the skin of streptozotocin (STZ)-induced type 1 diabetic rats, which are similar to those seen in vitamin A-deficient (VAD) rats. Retinoic acid (RA), the active form of vitamin A, promotes the production of collagen in dermis and induces cell growth and inhibition of epidermal differentiation in skin tissues. Normal skin function is maintained by the extracellular matrix (ECM)-degrading enzymes, matrix metalloproteinase (MMP) and hyaluronidase (HAase). This study is the first comparison of MMP and HAase activities in skin tissues of type 1 diabetic, VAD and RA-treated animal models. In skin tissues of type 1 diabetic and VAD rats or VAD mice, both MMP-2 and HAase activities increased as compared with controls. In contrast, MMP and HAase activities were reduced in the skin tissues of RA-treated mice. Blood retinol levels in type 1 diabetic rats were lower than controls. These results indicate a close relationship between type 1 diabetes and vitamin A-deficiency on MMP and HAase in skin tissues, suggesting that type 1 diabetic rats could be vitamin A-deficient. Vitamin A-derived RA might be a significant regulator of ECM-degrading enzyme expression and diabetic symptoms.

Daily oscillation of glutathione redox cycle is dampened in the nutritional vitamin A deficiency

Examples of hormonal phase-shifting of circadian gene expression began to emerge a few years ago. Vitamin A fulfills a hormonal function by binding of retinoic acid to its nuclear receptors, RARs and RXRs. We found retinoid- as well as clock-responsive sites on regulatory regions of Glutathione reductase (GR) and Glutathione peroxidase (GPx) genes. Interestingly, we observed retinoid receptors, as well as GSH, GR, and GPx, display daily oscillating patterns in the rat liver. We also found that feeding animals with a vitamin A-free diet, dampened daily rhythms of RARα and RXRβ mRNA, GR expression and activity, GSH, BMAL1 protein levels, and locomotor activity. Differently, day–night oscillations of RXRα, GPx mRNA levels and activity and PER1 protein levels, were phase-shifted in the liver of vitamin A-deficient rats. These observations would emphasize the importance of micronutrient vitamin A in the modulation of biological rhythms of GSH and cellular redox state in liver.

Implication of Vitamin A deficiency on vascular injury related to inflammation and oxidative stress. Effects on the ultrastructure of rat aorta

Vitamin A deficiency induces activation of NF-kB and impairs activities of antioxidant enzymes in aorta. We study the effect of vitamin A deficiency on the aorta histoarchitecture and the possibly contribution of its prooxidant and inflammatory effects to artery alterations. Twenty-one-day-old Wistar male rats were fed during 3months with vitamin A-deficient diet (-A, n=8) or the same diet containing 8mg of retinol palmitate/kg of diet (+A, control, n=8). In aortas, thiobarbituric reactive substances and reduced glutathione levels were measured by spectrophotometry. Expressions of TNF-alpha, NOX-2, VCAM-1, and TGF-beta1 were assessed by RT-PCR and Western Blot. The morphology of aorta was examined by light and transmission electron microscopy. In -A rats, high levels of TBARS in serum and aorta and low levels of GSH in aorta were found. An increased expression of TNF-alpha, NOX-2, VCAM-1, and TGF-beta1 in aorta from -A rats was observed. Examination of the intimal layer by light microscopy indicated the presence of an irregular surface in -A aortas. TEM studies showed large vacuoles and multivesicular bodies along the endothelium and also multivesicular bodies in the subendothelial space of aortas from -A rats. Furthermore, the histological appearance of internal elastic lamina was different from control. Small vesicles in the medial layer were observed in aortas from vitamin A-deficient rats. Vitamin A deficiency produces histoarchitectural alterations in aorta, which can be associated, at least in part, to the oxidative stress and inflammation induced by vitamin A deficiency.

Single oral dose of micellar β-carotene containing phospholipids improves β-carotene metabolism and plasma lipids in vitamin A-deficient rats

Vitamin A (VA) deficiency is still a major health problem in the developing world. It affects various cellular functions and causes hypolipidemic effects in the body. β-Carotene (BC)-rich foods are promising sources of VA. Phospholipids are reported to improve BC bioefficacy in normal rats, but whether they show similar effects during VA deficiency is unknown. To compare the BC metabolism and plasma lipid responses in VA-sufficient (+VA) and VA-deficient (-VA) rats after a single oral dose of micellar BC containing phospholipids. Groups of rats were fed with a VA-free diet and when they attained the weight-plateau stage of deficiency, both +VA and -VA rats were divided into 2 groups (phosphatidylcholine, PC and lysophosphatidylcholine, LPC). Each group was further divided into 4 subgroups (1, 2, 3, and 6 h; n = 5 rats/time point) and determined the BC metabolism and plasma lipid responses to a post-dose of micellar BC with phospholipids. Maximal plasma BC (pmol/mL) levels were observed at 2 h in PC (1330 ± 124) and at 1 h in LPC (1576 ± 144) groups of +VA rats, and at 3 h in the PC (1621 ± 158) and LPC (2248 ± 675) groups of -VA rats. Liver BC (pmol/g) was maximum at 1 h in the PC (218 ± 32) and LPC (249 ± 24) groups of +VA rats, and at 2 h in PC (228 ± 23) and at 3 h in LPC (277 ± 18) groups of -VA rats. Plasma and liver BC levels were significantly (P < 0.05) higher in -VA rats than +VA rats. Plasma retinyl palmitate (pmol/mL) was maximum at 3 h in PC (97 ± 18) and at 2 h in LPC (126 ± 14) groups of +VA rats, and at 2 h in the PC (92 ± 13) and LPC (134 ± 27) groups of -VA rats. The higher (P < 0.05) BC monoxygenase activity in -VA rats compared to +VA rats supports the BC bioefficacy. Plasma retinol level was improved in the PC and LPC groups, but the effect of LPC was higher (P < 0.05) than PC. Micellar phospholipids mitigate the VA deficiency-induced hypolipidemic effects. Micellar phospholipids improved BC metabolism and reinstated the hypolipidemic effects, perhaps by modifying the fat-metabolizing enzymes and repairing the altered intestinal membrane structure.

Regulation of renal sodium-dependent phosphate co-transporter genes (Npt2a and Npt2c) by all-trans-retinoic acid and its receptors

The type II sodium-dependent phosphate co-transporters Npt2a and Npt2c play critical roles in the reabsorption of Pi by renal proximal tubular cells. The vitamin A metabolite ATRA (all-trans-retinoic acid) is important for development, cell proliferation and differentiation, and bone formation. It has been reported that ATRA increases the rate of Pi transport in renal proximal tubular cells. However, the molecular mechanism is still unknown. In the present study, we observed the effects of a VAD (vitamin A-deficient) diet on Pi homoeostasis and the expression of Npt2a and Npt2c genes in rat kidney. There was no change in the plasma levels of Pi, but VAD rats significantly increased renal Pi excretion. Renal brush-border membrane Pi uptake activity and renal Npt2a and Npt2c expressions were significantly decreased in VAD rats. The transcriptional activity of a luciferase reporter plasmid containing the promoter region of human Npt2a and Npt2c genes was increased markedly by ATRA and a RAR (retinoic acid receptor)-specific analogue TTNPB {4-[E-2-(5,6,7,8-tetrahydro-5,5,8,8-tetra-methyl-2-naphtalenyl)-1-propenyl] benzoic acid} in renal proximal tubular cells overexpressing RARs and RXRs (retinoid X receptors). Furthermore, we identified RAREs (retinoic acid-response elements) in both gene promoters. Interestingly, the half-site sequences (5'-GGTTCA-3': -563 to -558) of 2c-RARE1 overlapped the vitamin D-responsive element in the human Npt2c gene and were functionally important motifs for transcriptional regulation of human Npt2c by ATRA and 1,25(OH)2D3 (1alpha,25-dihydroxyvitamin D3), in both independent or additive actions. In summary, we conclude that VAD induces hyperphosphaturia through the down-regulation of Npt2a and Npt2c gene expression in the kidney.